The existence of monoamine-producing neurons in the mammalian nervous system is now firmly established. Four groups of neurons have been characterized on the basis of neurotransmitter; dopamine, noradrenaline, adrenaline and serotonin neurons. In large part these are neurons with cell bodies in the brainstem or diencephalon. Dophamine neurons have restricted projections whereas adrenaline, noradrenaline and serotonin neurons all appear to distribute a widespread innervation pattern encompassing much of the neuraxis. This research program is directed toward analysis of two aspects of the biology of monoamine neurons. The first of these is an analysis of the discrete organization of the systems, particularly in regard to their termination within the telencephalon, diencephalon and brainstem. The second is in the development of monoamine innervation of these brain regions and the response of developing monoamine neurons to injury. Investigations in progress include an analysis of the noradrenaline and dopamine innervation of the basal forebrain and neocortex and an anatomical analysis of compensatory responses of central catecholamine neuron systems to injury as a function of age. BIBLIOGRAPHIC REFERENCES: Moore, R.Y. Synaptogenesis and the morphology of learning and memory. In: Rosenzweig, M.R. and Bennett, E.L. (Eds.), Neural Mechanisms of Learning and Memory, MIT Press, Cambridge, 1976, pp. 340-347. Halaris, A.E., Jones, B.E. and Moore, R.Y. Axonal transport in serotonin neurons of the midbrain raphe. Brain Research 107: 555-574, 1976.